Large energy users, such as the cement industry and refineries, object to the cost of the subsidy, through higher energy bills to fund the Renewable Heat Incentive that is meant to encourage heat pump installations.
The scheme, which gives around £1000 a year to households that generate their own green heat, was due to be introduced next spring.
The Daily Telegraph reported yesterday that unpublished trials conducted by the Energy Saving Trust, a government-funded body, show that the heat pumps are only "variably" effective at heating homes.
A study reveals that the green pumps do not always save money or carbon dioxide emissions, the Daily Telegraph said yesterday. Results of the EST trials, which have been running for a year, have been delayed and are not expected until later this autumn.
The newspaper cites government sources saying the renewable heat incentive in its current form is now likely to be either scrapped or scaled back amid concerns about its viability.